Spinal implants such as interbody fusion devices are used to treat degenerative disc disease and other damages or defects in the spinal disc between adjacent vertebrae. The disc may be herniated or suffering from a variety of degenerative conditions, such that the anatomical function of the spinal disc is disrupted. Most prevalent surgical treatment for these conditions is to fuse the two vertebrae surrounding the affected disc. In most cases, the entire disc will be removed, except for a portion of the annulus, by way of a discectomy procedure. A spinal fusion device is then introduced into the intradiscal space and suitable bone graft or bone substitute material is placed substantially in and/or adjacent to the device in order to promote fusion between two adjacent vertebrae.
Certain spinal devices for achieving fusion are also expandable so as to correct disc height between the adjacent vertebrae. Examples of expandable interbody fusion devices are described in U.S. Pat. No. 7,967,867, entitled “Expandable Interbody Fusion Device”, which issued on Jun. 28, 2011 (the '867 Patent), U.S. Pat. No. 8,641,769, entitled “Plastically Deformable Inter-Osseous Device”, which issued on Feb. 4, 2014 (the '769 Patent), U.S. Pat. No. 8,715,351, entitled “Expandable Interbody Fusion Device With Graft Chambers”, which issued on May 6, 2014 (the '351 Patent), and U.S. Pat. No. 9,078,767, entitled “Expandable Spinal Interbody Fusion Device”, which issued on Jul. 15, 2015 (the '767 Patent). The '867 Patent and the '351 Patent each disclose sequentially introducing in situ a series of elongate inserts referred to as wafers in a percutaneous approach to incrementally distract opposing vertebral bodies to stabilize the spine and correct spinal height, the wafers including features that allow adjacent wafers to interlock in multiple degrees of freedom. The '769 Patent discloses an expandable interbody fusion device that is plastically deformable from a smaller to a larger height in situ. The '767 patent discloses the introduction of one or more inserts into an interbody fusion device upon the expansion of the device by the creation of incremental spaces by an insertion instrument. The '867 Patent, the '769 Patent, the '351 Patent, and the '767 Patent are assigned to the same assignee as the present invention, the disclosures of these patents being incorporated herein by reference in their entirety.
With the use of expandable interbody fusion devices, it is desirable to provide an expandable trial or sizer instrument that would enable accurate sizing of the intradiscal space prior to insertion of the interbody fusion device. Certain expandable sizer instruments are known and are described in U.S. Pat. No. 8,277,456, entitled “Spinal-Column Distractor, which issued on Oct. 2, 2012, U.S. Pat. No. 7,087,055, entitled “Minimally Invasive Expanding Spacer and Method”, which issued on Aug. 8, 2006, and U.S. Pat. No. 6,582,451, entitled “Device for Use in Surgery”, which issued on Jun. 24, 2003. Nevertheless, there is still a need for an expandable sizer instrument that not only provides for proper spacing but that also is capable of withstanding clinically relevant axial compressive loading conditions of the spine in situ, that are particularly experienced within the intradiscal space between opposing vertebral bodies of the spine.